Motorcycle tire and pair of motorcycle tires

ABSTRACT

A motorcycle tyre has a tread band including a central portion and two shoulder portions arranged at axially opposite sides of the central portion. The central portion includes a first plurality of grooves extended according to a substantially longitudinal direction and alternatively arranged at opposite sides of the equatorial plane of the tyre. Each groove of the first plurality of grooves has a substantially curvilinear course such as to form a concavity. The central portion further includes a sub-portion substantially free of grooves placed astride the equatorial plane of the tyre. Each of the shoulder portions includes a second plurality of grooves arranged obliquely relative to the equatorial plane of the tyre.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 13/519,571, filed Jun. 27, 2012, which is a U.S.national phase entry under 35 U.S.C. § 371 of International PCTApplication No. PCT/IB2010/003341, filed Dec. 23, 2010, and claims thepriority of Italian Application No. RM2009A000688, filed Dec. 29, 2009,and U.S. Provisional Application No. 61/319,284, filed Mar. 31, 2010,all of which are incorporated herein by reference.

BACKGROUND Field

The present invention relates to motorcycle tyres. In particular, thepresent invention relates to tyres intended to be mounted on the frontwheel of motorcycles of the “Supersport” and/or “Sport Touring” segment,having large engine capacity (e.g. 600 cm, or higher), and/or high power(e.g. 170-180 hp or higher), also used on tracks.

Description of the Related Art

In recent times a trend has been observed to introduce in the marketmotorcycles for Supersport or Sport Touring use having high power. Forexample, motorcycles for road use having an engine capacity of 1000 cm³or higher, with powers of 180 hp, are in fact already available on themarket.

For ensuring such high performances, the tyres mounted on the wheels ofsuch motorcycles shall have excellent features as regards the grip tothe ground, so as to be able to effectively transfer the high tractiontorque to the ground, both in straight running and while accelerating onleaving a bend, as well as ensure an effective braking action. The gripbecomes a really critical issue above all when running on wet roadsurfaces.

For ensuring to the motorcyclist that such performances are reached in afully safe condition, the tyres shall ensure, together with a very goodgrip to the ground, behaviour stability both in straight running andwhile running on bends, particularly in conditions of highacceleration/deceleration. In fact, a stable behaviour of the tyreindicates its capacity to effectively dampen perturbations transmittedby the unevenness of the road surface while running, so that suchperturbations are not propagated to the motorcycle, thus compromisingthe driving stability.

Patent application EP 1826026 describes a tyre for motorcycles,especially adapted to be used as a front tyre of a racing motorcycle,comprising a tread portion provided with at least one pair ofcircumferential grooves extending generally in a circumferentialdirection of the tyre and oppositely disposed relative to the equatorialplane of the tyre, and a plurality of grooves inclined with respect tothe circumferential direction and extending from an outer side to aninner side in a width direction on the tread band. At least half of theinclined grooves extend across the equatorial plane of the tyre.According to EP 1826026, this choice allows a tyre with extremely lighthandling and stable when braking to be obtained.

FIGS. 1a and 1b show tread pattern portions respectively of the frontand rear Sportec™ M3 tyres. The Sportec™ M3 tyres, presently marketed byMetzeler™, are very much appreciated by motorcyclist keen on theSupersport segment.

SUMMARY

Looking for an improvement of the Sportec™ M3 tyre, the Applicant hasfound that by arranging a series of substantially longitudinal grooves,having a substantially curvilinear course, in a central portion of thetread band, and by leaving free of grooves a small portion of the treadband at the equatorial plane, it is possible to increase the surface ofthe footprint area of the tyre.

In particular, as shown hereinafter, it has been found that the increasein the surface of the footprint area is due to an increase in the widthof the same.

The Applicant believes that such an outcome is due to the fact that thelongitudinal and curvilinear grooves create a sort of “double hinge”,which allows the crown portion of the tyre to be moved radially in aregion away from the equatorial plane, so as to increase the compliancethereof. Moreover, the Applicant believes that the curvilineararrangement (i.e. an arrangement not aligned with the equatorial plane,except for portions of least longitudinal extension) of suchlongitudinal grooves allows the compliance of the crown region to beincreased in a controlled and not excessive way, so as not to causeeither the fatigue failure of the tread band at the grooves themselvesor an excessive leaning of the tyre on the footprint area. Thanks to theincrease in the surface of the footprint area, it is thus favoured thebehaviour stability of the tyre, particularly when conducted under amotorcycle in substantially straight running, without negativelyaffecting the graduality and/or the ease of making the motorcycle enterbends and/or mixed paths.

In particular, the increase in the surface of the footprint area isadvantageously achieved thanks to an increase in the width of thelatter, not to an increase in its length. In the Applicant's view, anexcessive length of the footprint area is in fact to be avoided, becauseit may cause local drops of the contact pressure and/or uneven wear, dueto an excessive and non linear returning action of the belt on the treadband in the outlet portion of the footprint area while running at smalldrift angles (as typically happens in straight running, which is neverexactly so).

In a first aspect thereof, the invention relates to a method forincreasing a footprint area of a motorcycle tyre in substantiallystraight running. The tyre comprises a tread band. The method comprises:

-   -   forming in a central portion of said tread band a first        plurality of grooves extended according to a substantially        longitudinal direction and alternatively arranged at opposite        sides of an equatorial plane of said tyre, wherein each groove        of said first plurality of grooves has a substantially        curvilinear course such as to form a concavity,    -   leaving free of grooves a sub-portion of said central portion        placed astride an equatorial plane of said tyre.

In a second aspect thereof, the invention relates to a motorcycle tyre,having a tread band comprising a central portion and two shoulderportions arranged at axially opposite sides of the central portion,wherein:

-   -   the central portion comprises a first plurality of grooves        extended according to a substantially longitudinal direction and        alternatively arranged at opposite sides of an equatorial plane        of said tyre, wherein each groove of said first plurality of        grooves has a substantially curvilinear course such as to form a        concavity;    -   the central portion comprises a sub-portion substantially free        of grooves placed astride an equatorial plane of said tyre;    -   each of said shoulder portions comprises a second plurality of        grooves arranged obliquely relative to the equatorial plane of        said tyre.

For the purposes of the present invention, by “tread pattern” it ismeant the representation of each point of the tread band (groovesincluded) on a plane perpendicular to the equatorial plane of the tyreand tangent to the maximum diameter of the tyre. In the representation:

-   -   in the lateral direction the distance of each point of the tread        band from the equatorial plane corresponds to the distance of        such point from the equatorial plane measured on the lateral        development of the band itself;    -   in the circumferential direction the distance between any two        points of the tread band corresponds to the distance between the        projections of the two points on the circumference corresponding        to the maximum diameter of the tyre, the projection being        obtained by means of radial planes passing at the two points.

Angle measurements, and/or linear quantities (distances, widths,lengths, etc.), and/or surfaces are to be intended as referred to thetread pattern as defined above.

Furthermore, referring to the angle of the grooves formed in the treadband with respect to the equatorial plane of the tyre, such angle is tobe intended, for each point of the groove, as referred to the angle(comprised, as absolute value, between 0° and 90°) defined by a rotationperformed starting from the equatorial plane and reaching the directiontangent to the groove passing at that point.

For the purposes of the present invention, the following definitions arefurther applied:

-   -   By “motorcycle tyre” it is meant a tyre having a high curvature        ratio (typically higher than 0.200), which allows high camber        angles (for example 50°-60°) to be reached when the motorcycle        runs on a bend.    -   By “equatorial plane” of the tyre it is meant a plane        perpendicular to the rotation axis of the tyre and dividing the        tyre into two symmetrically equal portions.    -   By “circumferential” or “longitudinal” direction it Is meant a        direction generically directed according to the rotation        direction of the tyre, or in any case only slightly inclined        with respect to the rotation direction of the tyre.    -   By “void to rubber ratio” it is meant the ratio between the        total surface of the notches of a determined portion of the        tread pattern of the tyre (possibly of the whole tread pattern)        and the total surface of the determined portion of the tread        pattern (possibly of the whole tread pattern).    -   By “lateral development” of the tread band it is meant the        length of the arc defining the radially outermost profile of the        tread band in a cross section of the tyre.    -   By “maximum longitudinal development” of the tread band it is        meant the length of development of the tread band in the        longitudinal direction at the radially outermost point of the        tread band.    -   By “curvature ratio” of the tyre it is meant the ratio between        the distance of the radially highest point of the tread band        from the maximum chord of the tyre, and the same maximum chord        of the tyre, in a cross section of the tyre.    -   By “longitudinal extension” of a groove it is meant the        extension of the projection in the circumferential direction of        the groove itself.    -   If not differently stated, by “extension” of a groove it is        meant the length of the groove measured along its course.    -   By “average inclination” or “average angle” of a groove it is        meant the arithmetical mean of the inclinations/angles of the        portions forming the groove compared to the equatorial plane of        the tyre. For grooves with curvilinear course, the average        inclination or average angle may be expressed as:

$\frac{1}{L}{\int_{0}^{L}{{\alpha(x)}{dx}}}$

-   -    where a(x) represents the angle of the groove at the        longitudinal “height” x and L represents the groove extension.    -   By “pitch” of the tyre it is meant the group of grooves and        rubber parts arranged so as to form a portion of the pattern        which is repeated on the tread band, substantially the same and        without interruption along the circumferential development of        the tread band. Along the circumferential development of the        tread band, the pitches may have different circumferential        lengths.    -   By “substantially longitudinal”, referring to a groove, it is        meant that such groove is arranged at an average angle with        respect to the equatorial plane of the tyre which is        substantially zero (e.g. of less than 10°).    -   By “substantially curvilinear” course of a groove it is meant a        course with substantial continuity of the derivative of the        curve representing the course itself. Typically, this is        achieved by means of a course without sharp points. The present        definition includes also the cases in which the groove is formed        by or comprises a sequence of short straight sections, provided        that the difference in the angular arrangement of such sections        is not too large (e.g. larger than 25°).

The present invention, in one or more preferred aspects, may compriseone or more of the features hereinafter presented.

Each groove of said first plurality of grooves may extend longitudinallyover at least 5% of a maximum longitudinal development of said treadband.

Said first plurality of grooves may be advantageously formed by acircumferential sequence of groove pairs comprising a first groove and asecond groove, wherein said first groove is arranged at one side of saidequatorial plane of the tyre and said second groove is arranged at theopposite side of said equatorial plane of the tyre.

A first end portion of said first groove and a second end portion ofsaid second groove may be advantageously arranged in a same transverseportion of said tread band. Such transverse portion may extendlongitudinally on said tread band up to a maximum corresponding to abouthalf the longitudinal development of said first or said second groove.

Preferably, the central portion of the tread band wherein theabove-mentioned first grooves are formed extends transversally over atmost 40% of the axial development of said tread band.

Preferably, the sub-portion of said central portion which is leftsubstantially free of grooves may extend transversally over at most 10%of an axial development of said tread band.

Advantageously, said sub-portion extends over at least 3% of an axialdevelopment of said tread band.

The tread band may have an overall void to rubber ratio greater thanabout 10%. Preferably, the overall void to rubber ratio is kept belowabout 25%.

The grooves of said second plurality of grooves may be arranged at aminimum average angle not lower than about 30° relative to theequatorial plane. In preferred embodiments, the grooves of said secondplurality of grooves are arranged at an average angle not greater than60° relative to the equatorial plane.

Said second plurality of grooves may for example comprise a set ofgroove pairs, wherein at least one extension of each groove pair of saidsecond plurality of grooves intersects a groove of said first pluralityof grooves.

Also the grooves of said second plurality of grooves may have asubstantially curvilinear course such as to form a concavity.

In particular, the grooves of said first plurality of grooves and thegrooves of said second plurality of grooves may be substantially formedby arcs of a circle. Such arcs of a circle may have substantially thesame bending radius both in the grooves of the first and in the groovesof the second plurality of grooves.

The bending radius may be for example between 90 mm and 250 mm.

In some embodiments, the concavity of the grooves of said secondplurality of grooves is directed according to a direction opposite to apreferred rolling direction of said tyre.

In alternative embodiments, the concavity of the grooves of said secondplurality of grooves is directed according to a preferred rollingdirection of said tyre.

In some embodiments, the concavity of the grooves of said firstplurality of grooves is directed toward the equatorial plane of saidtyre.

In alternative embodiments, the concavity of the grooves of said firstplurality of grooves is directed according to a direction opposite tothe equatorial plane of said tyre.

The invention may thus comprise a pair of motorcycle tyres, comprising afirst tyre configured with the concavity of the grooves of said secondplurality of grooves directed according to a direction opposite to apreferred rolling direction of said first tyre, adapted to be mounted ona rear wheel of said motorcycle, and a second tyre configured with theconcavity of the grooves of said second plurality of grooves directedaccording to a preferred rolling direction of said second tyre, adaptedto be mounted on a front wheel of said motorcycle.

The invention may further comprise, additionally and/or alternatively, apair of motorcycle tyres, comprising a first tyre configured with theconcavity of the grooves of said first plurality of grooves directedtoward the equatorial plane of said first tyre, adapted to be mounted ona rear wheel of said motorcycle, and a second tyre configured with theconcavity of the grooves of said first plurality of grooves directedaccording to a direction opposite to the equatorial plane of said secondtyre, adapted to be mounted on a rear wheel of said motorcycle.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the tyre of the present inventionshall become clearer from the following detailed description of somepreferred embodiments thereof, made hereafter for indicative andnon-limiting purposes with reference to the accompanying drawings. Insuch drawings:

FIGS. 1a and 1b show portions of the tread pattern of known tyres, asdescribed above;

FIG. 2 shows a radial sectional view of a tyre according to theinvention;

FIG. 3 shows a portion of the plan development of a portion of the treadband of a tyre according to a first embodiment of the invention;

FIG. 4 shows a portion of the plan development of a portion of the treadband of a tyre according to a second embodiment of the invention;

FIG. 5 shows a portion of the plan development of a portion of the treadband of a tyre according to a third embodiment of the invention;

FIG. 6 shows a portion of the plan development of a portion of the treadband of a tyre according to a fourth embodiment of the invention;

FIG. 7 shows a comparison of the trend of the length of the footprintarea as a function of the load in a known tyre (FIG. 1a ) and in a tyreaccording to the invention (FIG. 3);

FIG. 8 shows a comparison of the trend of the width of the footprintarea as a function of the load in a known tyre (FIG. 1a ) and in a tyreaccording to the invention (FIG. 3).

DETAILED DESCRIPTION

Referring to FIG. 2, a tyre for motorcycle wheels according to thepresent invention is globally indicated at 100. In particular, the tyreis preferably intended to be used on the front or rear wheel of amotorcycle for the sport or Supersport segment.

An equatorial plane X-X and a rotation axis Z are defined in the tyre100. Moreover, there are defined a circumferential or longitudinaldirection and an axial, or transverse, or lateral direction,perpendicular to the equatorial plane X-X.

The tyre 100 comprises a carcass structure 2 including at least one ortwo carcass plies 3.

The carcass structure 2 is preferably lined on its inner walls with asealing layer 16, also called “liner”, essentially consisting of a layerof an airproof elastomeric material, adapted to ensure the tight seal ofthe tyre itself after it has been inflated.

The carcass ply/plies 3 is/are engaged, at the respective axiallyopposite lateral edges 3 a, with respective annular reinforcingstructures 4 intended to hold the tyre on a corresponding fitting rim.The annular reinforcing structures 4 are typically called “bead cores”.

A tapered elastomeric filler 5 taking up the space defined between thecarcass ply or plies 3 and the respective turned lateral edge 3 a of thecarcass ply or plies 3 is applied onto the radially outer perimeter edgeof the bead cores 4.

In an alternative embodiment, not shown, the carcass ply has itsopposite lateral edges associated without a turn-up with special annularreinforcing structures provided with two metal annular inserts. In thiscase, a filling of elastomeric material can be arranged in an axiallyouter position with respect to the first annular insert. The secondannular insert is instead arranged in an axially outer position withrespect to the end of the carcass ply. Finally, in a axially outerposition with respect to said second annular insert, and not necessarilyin contact with the same, a further filling can be provided whichfinishes the formation of the annular reinforcing structure.

The region of the tyre comprising the bead ring 4 and the filler 5defines the so-called “bead”, globally indicated at 15 in FIG. 2, whichis intended for anchoring the tyre to a corresponding fitting rim, notshown.

A belt structure 6 is provided in a radially outer position with respectto the aforementioned carcass structure.

A tread band 8, at which the tyre 1 contacts the ground, is provided ina radially outer position with respect to the belt structure 6.

The tyre may further comprise a pair of sidewalls 2 a laterally appliedto the carcass structure 2 at axially opposite sides of the equatorialplane X-X. The sidewalls extend from the tread band 8 to the bead 15 ofthe tyre.

The tyre 100 of the present invention is characterised by a hightransverse curvature and lowered sidewalls.

The transverse curvature of a tyre is defined by the particular value ofthe ratio between the distance ht (FIG. 1) of the top of the tread bandfrom the line b-b passing through the ends O of the tread, measured onthe equatorial plane X-X, and the distance wt between said ends of thetread band. Should the ends of the tread band not be easilyidentifiable, for example due to the lack of a precise reference, suchas for example the edge indicated at O in FIG. 2, the length of themaximum chord of the tyre can certainly be taken as the distance wt.

The value of the aforementioned transverse curvature is called“curvature ratio” of the tyre.

The tyre 100 of the present invention preferably has a curvature ratiogreater than or equal to 0.2, preferably greater than or equal to 0.25.For front tyres, the curvature ratio can also be greater than 0.30. Sucha curvature ratio is typically less than or equal to 0.8, preferablyless than or equal to 0.5.

With regards to the sidewalls, on the other hand, the tyre of thepresent invention is preferably a tyre with particularly low sidewalls.By tyres with low or lowered sidewalls in the present description aremeant tyres wherein the ratio between the distance (H-ht) and the heightH, measured on the equatorial plane X-X between the top of the treadband and the fitting diameter, defined by the reference line L passingthrough the beads of the tyre, is less than 0.6, more preferably lessthan 0.5.

Each carcass ply 3 is preferably made from an elastomeric material andcomprises a plurality of reinforcing elements (not shown) arrangedparallel to one another.

The reinforcing elements included in the carcass plies 3 preferablycomprise textile cords selected from those usually adopted in themanufacture of carcasses for tyres, for example nylon, rayon, lyocell,aramid, PET, PEN, with an elementary thread having a diameter between0.35 mm and 1.5 mm. The reinforcing elements in the carcass ply 3 arepreferably arranged in a substantially radial direction, i.e. accordingto an angle between 650 and 1100, more preferably between 80° and 100°,with respect to the equatorial plane X-X.

The belt structure 6 preferably comprises one or more rubberized cords7, arranged parallel to one another and in side-by-side relationship inthe axial direction on the crown portion 16 of the carcass structure 2,so as to form a plurality of coils 7 a. Such coils are substantiallyoriented according to the circumferential direction of the tyre(typically with an angle between 0° and 5° with respect to theequatorial plane X-X of the tyre), such a direction usually being knownas “at zero degrees” with reference to how it lies with respect to theequatorial plane X-X of the tyre. The aforementioned coils preferablyextend over the entire crown portion 16 of the carcass structure 2.

Preferably, the belt structure 6 is formed by a single cord 7, or by arubberized fabric strip comprising preferably up to five cords arrangedin side-by-side relationship. The cord or strip is spirally wound fromone end to the other on the crown portion 16 of the carcass structure 2.

Alternatively, the belt structure 6 may comprise at least two radiallysuperimposed layers, each consisting of elastomeric material reinforcedwith cords arranged parallel to one another. The layers are arranged sothat the cords of the first belt layer are oriented obliquely (forexample at an angle between 15° and 40°) with respect to the equatorialplane of the tyre, whereas the cords of the second layer also have anoblique orientation, but symmetrically crossed with respect to the cordsof the first layer, so as to form the so-called “cross-belt”.

The cords 7 of the belt structure 6 are textile or metal cords.

Preferably, for the use in a belt at zero degrees, such cords are madeby steel wires with high carbon content, i.e. steel wires with a carboncontent at least equal to 0.7%. Preferably, such cords 7 are metal cordsmade from steel of the high elongation (HE) type. The high elongation(HE) cords typically have an ultimate tensile strength higher than 3%.Typically, they have a load-elongation diagram comprising a curvilinearportion arranged between two substantially straight portions havingdifferent inclinations with respect to the axes of the diagram.

When textile cords are used, these can be made from a synthetic fiber,for example nylon, rayon, PEN, PET, preferably a synthetic fiber withhigh modulus, in particular synthetic aramid fiber (for example Kevlar®fibers). Alternatively, hybrid cords can be used comprising at least onethread with low modulus, i.e. with a modulus not greater than 15000 N/nm(for example nylon or rayon), intertwisted with at least one thread withhigh modulus (for example Kevlar®), i.e. with a modulus not smaller than25000 N/mm².

The belt structure 6 may also comprise one or more support layers 17made from elastomeric material, interposed between the layer of cords 7and the carcass ply 3 and on which the coils 7 a are wound. Suchlayer(s) may extend on a surface having an axial extension substantiallycorresponding to the surface on which the coils 7 a extend.

In a preferred embodiment of the tyre 100 of the present invention, alayer 17 is used comprising short aramid fibres, for example made fromKevlar®, dispersed in the elastomeric material.

In a further embodiment (not shown), in the belt structure 6 it can beused, additionally or alternatively to the layer reinforced with aramidfibres described above, at least a layer reinforced with textile cords(totally similar to the cords that can be used in the carcass structure3), with a substantially radial orientation (for example between 65° and110°). Such a layer extends at least on the crown portion 16 of the tyre100, or also on a larger portion, but without a turn-up about the beadrings 4.

A tread pattern is formed on the tread band 8. Such pattern is definedby a plurality of grooves differently arranged along the circumferentialand axial development of the tread band 8. Within a pitch of the treadpattern, such grooves define a module which is repeated substantiallythe same along the circumferential direction of the tyre 100.

In particular, in the tyre of the present invention the pattern formedon the tread band 8 can be divided into a central portion A and twoshoulder portions B. The central portion A may extend over up to the 40%of the axial development of the tread band 8.

In the tyre section shown in FIG. 2 three grooves 20, 21, 26 are shown.The groove 20 lies in the central portion A, whereas the grooves 21, 26lie in the shoulder portions B.

FIGS. 3-6 show portions of some embodiments of a tread pattern that canbe used in a tyre according to the invention. Arrow F indicates thepreferred tyre rolling direction. In particular, the embodiments ofFIGS. 3 and 6 can be preferably used for rear tyres, whereas theembodiments of FIGS. 4 and 5 can be preferably used for rear tyres.

A tread pattern as in the examples shown in FIGS. 3-6 globally defineson the tread band 8 a void to rubber ratio higher than or equal to about10%, preferably higher than or equal to about 12%. Preferably, the voidto rubber ratio is lower than 25%.

In FIGS. 3-6 the central portion A, arranged at the equatorial planeX-X, and the two shoulder portions B, arranged at axially opposite sidesof the central portion A, can be identified.

The central portion A is intended to contact the road surface when themotorcycle runs on a straight path or with a slight lean, whereas theshoulder portions B are intended to contact the road surface when themotorcycle runs on a bend with a more marked lean.

Preferably, the central annular portion A has an axial extension at mostequal to 40% of the lateral development of the tread band 8.

The central portion A has a plurality of first grooves 20 separate fromone another. Preferably, the void to rubber ratio in the central portionA is between about 8% and about 15%.

The first grooves 20 extend according to a substantially longitudinaldirection. Moreover, the grooves extend with a substantially curvilinearcourse. The curvilinear course of the first grooves 20 defines aconcavity, which in the embodiments of FIGS. 3, 5, 6 is directed towardsthe equatorial plane X-X, whereas in the embodiment of FIG. 4 isdirected according to a direction opposite to the equatorial plane X-X.

In a preferred embodiment, the first grooves 20 have a coursesubstantially corresponding to an arc of a circle. Preferably, thebending radius of such arc of a circle is between about 90 mm and about250 mm.

Preferably, the first grooves 20 extend over at least about 5% of themaximum longitudinal development of the tread band 8. They are thereforegrooves with a substantial length, typically of the order of thelongitudinal dimension of the footprint area formed by the tyre under anominal load (about 200-250 kg for the Supersport and/or Sport Touringsegment). This feature of the substantially curvilinear first grooves20, together with their substantially longitudinal course, allows waterto be drained during straight running on wet asphalt (or, in general,ground). Furthermore, it has been found that such arrangement of thefirst grooves 20 allows reducing the noise caused by the same when thetyre is rolling. Preferably, the first grooves 20 extend at most overabout 25%, more preferably over about 10% of the maximum longitudinaldevelopment of the tread band 8.

The substantially longitudinal extension of each of the substantiallycurvilinear first grooves 20 makes a symmetry axis of the extension ofsuch grooves to be oriented according to an angle substantiallyperpendicular to the equatorial plane X-X (for example with a maximumdeviation lower than about 10° with respect to a direction perpendicularto the equatorial plane X-X).

For the purposes of the present invention, the symmetry axis of theextension of a groove may correspond to the direction perpendicular toone of the lines defining the general course of the groove itself,passing through the point which half divides the groove itself. The linedefining the general course of a groove may be selected for exampleamong one of the radially outer edges of the groove, the centre line ofthe groove and/or the line of maximum depth of the groove. In FIGS. 3-6such general course is shown, as an example and for the sake of clarityonly on some of the grooves of each pattern portion, by a dashed centreline.

In the embodiments shown in FIGS. 3-6, each pitch of the tyre comprisesa pair of grooves 20, arranged at opposite sides with respect to theequatorial plane X-X.

The first grooves 20 of each pair are preferably staggered in thecircumferential direction. In other words, the first grooves 20alternate at opposite sides with respect to the equatorial plane X-Xalong the circumferential direction of the tyre, such that a firstgroove 20 arranged at one side with respect to the equatorial plane X-Xis followed by a subsequent first groove 20 arranged at the oppositeside with respect to the equatorial plane X-X.

While alternating at one side and the other of the equatorial plane X-X,the ends proximal with each other of two consecutive first grooves 20may preferably be arranged in a same transverse portion of the treadband 8. In other words, it may be preferably provided that the endportions of two consecutive first grooves 20 can overlap longitudinally(remaining however axially spaced apart). The overlapping canadvantageously extend even up to half the longitudinal development ofone of the first grooves 20.

This allows at least one of the first grooves 20 to be always keptwithin the footprint area during straight running, so as to ensure gooddrainage when running on wet grounds.

The arrangement of the first grooves 20 in the central portion A of thetread band 8 is such that a central annular sub-portion (for the sake ofclarity shown only in FIG. 3 by means of the shaded portion indicated atS) is formed astride the equatorial plane X-X, which have a void torubber ratio substantially equal to zero. In other words, the firstgrooves 20 do not cross the equatorial plane X-X, but lie away from thesame substantially along their entire extension, from one end to theother. In the embodiments shown in FIGS. 3, 5, 6 each of the firstgrooves 20 has its ends near the equatorial plane X-X, while the centralportion lies farther from it. On the contrary, in the embodiment of FIG.4 the ends of the first grooves 20 lie farther from the equatorial planeX-X compared to the central portion.

The central annular sub-portion S with substantially zero void to rubberratio extends transversally over a portion of the axial development ofthe tread band between about 3% and about 10%.

Keeping a portion substantially free of grooves at the equatorial planeX-X allows the formation of a closed ring in the tread band with anextremely high stiffness in this portion, so that in straight running athigh speed it is possible to effectively transfer to the ground thetraction torque while accelerating and the braking torque whiledecelerating, at the same time ensuring an excellent stability to themotorcycle. This choice is thus extremely advantageous for the use bothon a front and on a rear tyre.

Preferably, the first grooves 20 have a variable width along theirextension.

In particular, in the embodiments of FIGS. 3 and 6, the width of thefirst grooves 20 increases in a direction opposite to the preferredrolling direction F of the tyre. This choice may be convenient forincreasing the water drainage in a rear tyre during straight running onwet grounds. The width of the first grooves 20 may, for example, varyfrom a minimum of 2-4 mm to a maximum of 6-8 mm.

In the embodiments of FIGS. 4 and 5, the width of the first grooves 20increases in the preferred rolling direction F of the tyre. This choicemay be convenient in a front tyre, for effectively breaking and openingwater films and/or layers during straight running on wet grounds.

The Applicant has found that the arrangement described above of thefirst grooves 20 allows the surface of the footprint area of the tyre tobe increased. In particular, as it shall be shown hereinafter by meansof an example, it has been found that the increase in the surface of thefootprint area is due to an increase of the width of the same. TheApplicant believes that this may be due to the fact that the firstgrooves 20 create a sort of “hinge”, which allows the crown portion ofthe tyre to be moved radially in a region away from the equatorialplane, so as to increase the compliance thereof. Moreover, the Applicantbelieves that the curvilinear arrangement (i.e. an arrangement notaligned with the equatorial plane X-X of the tyre, apart from portionsof least longitudinal extension) of the longitudinal grooves 20 allowsthe compliance of the crown region to be increased in a controlled andnot excessive way, so as not to cause fatigue failure of the tread bandat the first grooves 20 themselves. In the preferred embodiment shown inFIGS. 2-6, the compliance of the central portion A of the tyre crowndetermined by the presence of the first grooves 20 synergicallycooperates with a further source of compliance introduced, in the sameportion of the tyre, by the presence of a belt structure at zero degrees6 under the tread band 8. According to tests performed by the Applicant,it has been found that tyres having this configuration achieve anexcellent behaviour stability in straight running, together with aproper graduality when approaching a bend and/or during repeateddirection changes. These results have been obtained using such aconfiguration for both the front tyre and the rear tyre.

Referring again to FIGS. 3-6, each shoulder portion B has a plurality ofsecond grooves 21, 26 extending substantially transversally on the treadband 8. The second grooves 21, 26 are arranged so as to be axially inside-by-side relationship with the first grooves 20. In particular, theaxially inner ends of the second grooves 21, 26 may either approach thefirst grooves 20 without intersecting them (as in the embodiments shownin FIGS. 3, 4 and 6) or terminate into the first grooves 20 themselves(as in the embodiment shown in FIG. 5). In any case, at least acontinuation of the second grooves 21, 26 intersects the first grooves20, as shown in FIGS. 3-6 by the dashed lines represented for a group ofgrooves 20, 21, 26 (in each figure).

In the preferred embodiments shown in FIGS. 3-6 the second grooves 21,26 are divided into pairs. Each pair of second grooves 21, 26 isassociated with a respective first groove 20 as mentioned above.

The intersection between the continuation of a pair of second grooves21, 26 (or the pair of second grooves 21, 26 itself) and a first groove20 preferably divides the latter into three portions with substantiallythe same longitudinal extension.

Preferably, the second grooves 21, 26 are arranged on the tread band 8with a substantially curvilinear course. In general, the second grooves21, 26 may have an average inclination between about 30° and about 90°,preferably between about 30° and about 60° with respect to theequatorial plane X-X.

In the embodiments shown in FIGS. 3 and 6, the concavity formed by thecurvilinear course of the second grooves 21, 26 is directed in adirection opposite to the preferred rolling direction F. On thecontrary, in the embodiments shown in FIGS. 4 and 5, the concavityformed by the curvilinear course of the second grooves 21, 26 isdirected according to the preferred rolling direction F.

In a preferred embodiment, the second grooves 21, 26 have a coursesubstantially corresponding to an arc of a circle. Preferably, thebending radius of such arc of a circle is between about 90 mm and about250 mm.

The arcs of a circle forming, in preferred embodiments, the first andthe second grooves 20, 21, 26 may advantageously be similar with oneanother. In practice, for grooves having a considerable extension on thetread band, such a substantial similarity may correspond to differencesup to about 50%-60% of the larger bending radius. In fact, arcs of acircle with bending radius respectively equal to e.g. 100 mm and 180 mmmay be practically non-distinguishable at sight, without using measuringinstruments.

The Applicant believes that the arrangement of extended grooves havingsubstantially the same bending radius (within the meaning indicatedabove) improves the distribution of the elastomeric material forming thetread band during the tyre moulding and vulcanization, so as to obtain abetter quality and uniformity of the tread band itself in the mouldedand vulcanized tyre. In fact, similar bending radiuses for the elementsprojecting from the surface of the mould and intended for forming thegrooves, displace substantially in the same way the green elastomericmaterial during moulding, thus avoiding undesired accumulation ofmaterial.

Preferably, the second grooves 21, 26 have a variable width. Inparticular, the second grooves 21, 26 may have a width which increasesfrom the axially innermost end towards the axially outermost end. Thewidth of the second grooves 21, 26 may vary e.g. from a minimum of 2-4mm to a maximum of 6-8 mm.

Besides the above-mentioned first and second grooves 20, 21, 26, thetread band may comprise further grooves and/or set of grooves, based onthe technical or aesthetic requirements of the tyre.

As an example, in the embodiments shown in FIGS. 3 and 4, a set of shortcuts is added at the axially outermost region of the shoulder portionsB. In particular, the short cuts 27 are formed substantially at acontinuation of the second grooves 21, 26. Such short cuts 27 mayimprove the tyre behaviour while running on a bend with maximum lean onwet grounds and/or make easier the warming of the tread band in theaxially outermost portion due to compound deformation.

In the embodiment of FIG. 4, in the shoulder portions B it is furtherformed a set of third grooves 28 alternating with the second grooves 21,26. The third grooves 28 have a lower extension than the extension ofthe second grooves 21, 26. Also these grooves may improve the tyrebehaviour, particularly in a front tyre, when running on a bend on wetgrounds.

In the embodiments of FIGS. 5 and 6, a set of groove pairs 29 isalternated, in the shoulder portions B, with the second grooves 21, 26.In the embodiment of FIG. 6 the grooves of the groove pair 29 have anextension different from each other. Also these grooves may improve thetyre behaviour, particularly in a front tyre, when running on a bend onwet grounds.

In both the embodiments of FIGS. 5 and 6 a plurality of grooves 30 isfurther formed in transition region between the central portion A andthe shoulder portions B of the tread band 8. Such grooves 30 may beformed for locally modifying the void to rubber ratio in the tread band8, so as to improve the tyre behaviour graduality when approaching abend and/or when running with frequent direction changes.

FIGS. 7 and 8 show the results of static deflection tests at differentloads on a tyre having a tread band as in FIG. 1b (comparison) and atyre having a tread band as in FIG. 3 (invention). Both tyres had size180/55 R17 and were different only in the tread band (same innerstructure, same compound of the tread band). During the tests the lengthand width of the footprint area, i.e., respectively, the longitudinaldimension and the transverse dimension of the footprint area, have beenmeasured. FIGS. 7 and 8 show the behaviour, respectively, of the lengthand of the width of the footprint area for the comparison tyre (dashedline, triangles) and the tyre of the invention (continuous line,squares).

As apparent from FIGS. 7 and 8, while the length of the footprint arearemains substantially the same for all the tested load values (FIG. 7),there is a significant increase in the width of the footprint area,particularly starting from loads of about 200 kg. Such load valuebasically corresponds the nominal load of tyres for motorcycles of theSupersport and/or Sport Touring segment.

In the following, in tables 1 and 2, the results obtained in drive testsperformed with different tyre sets mounted on the wheel of a motorcycle(Yamaha YZF R1) representative of the Supersport segment, but suitablefor providing useful indication of the behaviour stability also for theSport Touring segment, are reported.

In table 1 a comparison between a set comprising a front tyre having atread pattern as in FIG. 1a (comparison) and a set comprising a fronttyre having a tread pattern as in FIG. 4 (invention) is reported. Bothtyres had the same size (120/70 R17), as well as the same structure andtread band compound.

In table 2 a comparison between a set comprising a rear tyre having atread pattern as in FIG. 1b (comparison) and a set comprising a reartyre having a tread pattern as in FIG. 3 (invention) is reported. Bothtyres had the same size (190/55 R17), as well as the same structure andtread band compound.

In tables 1 and 2 the assessments obtained from the tyre according tothe invention as compared with the comparison tyre are reported forparameters typical for a drive on mixed paths (steering promptness,handling during changes of direction, lateral thrust while leaning,insertion into a bend at high speed, graduality while leaning) andparameters typical for a drive on straight paths (centering, reactivityto speed changes, compliance/behaviour stability). The assessments areexpressed on a scale ranging from 1 to 5, where 3 represents anacceptable behaviour and 4 represents an excellent behaviour.

TABLE 1 (front) 1st Set 2nd Set (comparison) (invention) Promptness 3.904.00 Handling 3.80 4.00 Thrust 4.00 4.25 Insertion at high speed 4.004.25 Graduality while leaning 4.00 4.15 Centering 4.15 4.25 Reactivity4.00 4.15 Yielding 4.00 4.15

TABLE 2 (rear) 1st Set 2nd Set (Comparison) (invention) Promptness 3.904.00 Handling 3.80 3.90 Thrust 4.00 4.25 Insertion at high speed 4.004.15 Graduality while leaning 4.00 4.15 Centering 4.15 4.25 Reactivity4.00 4.00 Yielding 4.00 4.00

As apparent from the tables reported above, the tyre according to theinvention has globally a better behaviour, both in the case of the fronttyre and in the case of the rear tyre, compared to the already excellentcomparison tyre considered.

The tests described above have been carried out on dry road ground. Aseries of tests performed on wet road ground showed a similar behaviourfor the two kind of tyres.

The overall results of the tests thus showed a global improvement of thetyre of the invention compared to the comparison tyre during straightrunning, without negatively affecting adherence and/or the behaviour onwet grounds. Such a result is remarkable and surprising taking intoaccount that the introduction of the sub-portion free of grooves at theequatorial plane might have instead caused a worsening of adherence andstability on wet grounds, particularly in straight running. TheApplicant believes that the increased leaning corresponding to theincrease in the width of the footprint area allowed this possibledrawback to be avoided, also improving the stability in straight runningand, above all, the promptness and handling on mixed paths.

The present invention has been described with reference to someembodiments thereof. Many modifications can be made in the embodimentsdescribed in detail, still remaining within the scope of protection ofthe invention, defined by the following claims.

The invention claimed is:
 1. A motorcycle tyre comprising a tread bandcomprising a central portion and two shoulder portions arranged ataxially opposite sides of the central portion, wherein: the centralportion comprises a first plurality of grooves extended according to asubstantially longitudinal direction and alternatively arranged atopposite sides of an equatorial plane of said tyre, wherein each grooveof said first plurality of grooves has a substantially curvilinearcourse thereby forming a concavity; the central portion comprises asub-portion substantially free of grooves placed astride an equatorialplane of said tyre; each of said shoulder portions comprises a secondplurality of grooves arranged obliquely relative to the equatorial planeof said tyre; said second plurality of grooves comprises a set of groovepairs, wherein at least one extension of each groove pair of said secondplurality of grooves intersects a groove of said first plurality ofgrooves; wherein each of said groove pairs is associated with arespective groove of said first plurality of grooves; wherein the treadband comprises cuts positioned at axially outermost portion regions ofthe shoulder portions; wherein each cut is not connected to a groove ofthe second plurality of grooves; wherein each cut is formed adjacent toa groove of the second plurality of grooves; wherein each cut issubstantially shorter in length than the grooves of the second pluralityof grooves; and wherein each cut is inclined in an opposite direction,relative to the equatorial plane, than a respective adjacent secondgroove.
 2. The tyre according to claim 1, wherein at least one extensionof each groove pair of said second plurality of grooves intersects thegroove of said first plurality of grooves at a portion spaced apart fromthe ends of the groove of said first plurality of grooves.
 3. The tyreaccording to claim 1, wherein each groove of said first plurality ofgrooves extends longitudinally over at least 5% of a maximumlongitudinal length of said tread band.
 4. The tyre according to claim1, wherein said first plurality of grooves is formed by acircumferential sequence of groove pairs comprising a first groove and asecond groove, wherein said first groove is arranged at one side of saidequatorial plane of the tyre and said second groove is arranged at theopposite side of said equatorial plane of the tyre.
 5. The tyreaccording to claim 1, wherein a first end portion of said first grooveand a second end portion of said second groove are arranged in a sametransverse portion of said tread band.
 6. The tyre according to claim 5,wherein said transverse portion extends longitudinally on said treadband over at most half a longitudinal length of said first or saidsecond groove.
 7. The tyre according to claim 1, wherein said centralportion extends transversally over at most 40% of an axial length ofsaid tread band.
 8. The tyre according to claim 1, wherein saidsub-portion of said central portion extends transversally over at most10% of an axial length of said tread band.
 9. The tyre according toclaim 1, wherein said sub-portion of said central portion extendstransversally over at least 3% of an axial length of said tread band.10. The tyre according to claim 1, wherein the tread band has a void torubber ratio between 10% and 25%.
 11. The tyre according to claim 1,wherein the grooves of said second plurality of grooves are arranged atan average angle not less than 30° relative to the equatorial plane ofsaid tyre.
 12. The tyre according to claim 1, wherein the grooves ofsaid second plurality of grooves are arranged at an average angle notgreater than 60° relative to the equatorial plane of said tyre.
 13. Thetyre according to claim 1, wherein the grooves of said second pluralityof grooves have a substantially curvilinear course thereby forming aconcavity.
 14. The tyre according to claim 13, wherein the grooves ofsaid first plurality of grooves and the grooves of said second pluralityof grooves are substantially formed by arcs of a circle, wherein saidarcs of a circle have substantially a same bending radius both in thegrooves of the first and in the grooves of the second plurality ofgrooves.
 15. The tyre according to claim 14, wherein said bending radiusis between 90 mm and 250 mm.
 16. The tyre according to claim 14, whereinthe concavity of the grooves of said second plurality of grooves isdirected according to a direction opposite to a preferred rollingdirection of said tyre.
 17. The tyre according to claim 14, wherein theconcavity of the grooves of said second plurality of grooves is directedaccording to a preferred rolling direction of said tyre.
 18. The tyreaccording to claim 1, wherein the concavity of the grooves of said firstplurality of grooves is directed toward the equatorial plane of saidtyre.
 19. The tyre according to claim 1, wherein the concavity of thegrooves of said first plurality of grooves is directed according to adirection opposite to the equatorial plane of said tyre.
 20. The tyreaccording to claim 1, wherein the shoulders portions comprise a set ofthird grooves alternating with the second grooves in a tyre capable ofbeing adapted for mounting on a front wheel of said motorcycle.
 21. Thetyre according to claim 20, wherein the third grooves have a lowerextension than the extension of the second grooves.